EMF and internal resistance

Question 1

What is internal resistance?

Answer 1

resistance within the source of electricity

due to the opposition to the flow of charge through the source

this causes electrical energy produced by the source to be dissipated inside the source

Question 2

What is EMF?

Answer 2

the electromotive force of the source is the electrical energy per unit of charge produced by the source

Question 3

What is the pd across the terminals?

Answer 3

pd across teh terminals of the source is the electrical energy per unit charge delivered by the source when it is in a circuit

the terminalk pd is less than the emf whenever current passes through the source due to its internal resistance

Question 4

What is internal resistance in terms of potential difference?

Answer 4

internal resistance of a source is the loss of potential difference per unit of current in the source when current passes through the source

Question 5

How is power supplied by the cell calculated?

Answer 5

I (emf) = I^2R + I^2r power supplied by the cell = power delivered to R + power wasted in the cell due to its internal resistance

Question 6

How can pd across the terminals be measured?

Answer 6

connecting a high-resistance voltmeter directly across the terminals of the cell

current is controlled by using a variable resistor, measured using ammeter

Question 7

What happens as the terminal pd decreases?

Answer 7

current increases because the lost pd increases as the current increases

Question 8

When is the terminal pd equal to the cell emf?

Answer 8

at zero current because lost pd is zero at zero current

Question 9

What are the characteristics of a graph that plots terminal pd versus current?

Answer 9

straight line with negative gradient this is seen by rarranging the equation emf = IR + Ir to become IR = emf - Ir because IR represents the terminal pd

Question 10

How is EMF measured directly?

Answer 10

voltmeter across terminals with nothing connected to the batter / no additional load

Question 11

Describe how you would obtain a set of reading to investigate the relationship between efficiency and the resistance of the external resistor

state any precaution you would take to ensure your reading are reliable

Answer 11

vary external; resistor and measure new value for V for at least 7 different values

switch off between readings, take repeats

VI / emf I